MACAM PROSES BIOLOGIS

PENGOLAHAN BIOLOGIS UNTUK LIMBAH CAIR Peraturan tentang baku mutu air limbah. Beberapa perlakuan dibutuhkan untuk memenuhi baku mutu: Perlakuan primer Penghilangan fisik bahan tersuspensi. Perlakuan sekunder Degradasi oleh mikroba untuk menghilangkan senyawa organik terlarut. Perlakuan tersier Pemisahan bahan terendapkan.

Primary Settling Basins

Primary Settling

Primary Settling Tank Design Size rectangular: 3-24 m wide x 15-100 m long circular: 3-90 m diameter Detention time: 1.5-2.5 hours Overflow rate: 25-60 m3/m2·day Typical removal efficiencies solids: 50-60% BOD5: 30-35%

Secondary Treatment Provide BOD removal beyond what is achieved in primary treatment removal of soluble BOD additional removal of suspended solids Basic approach is to use aerobic biological degradation: organic carbon + O2 → CO2 Objective is to allow the BOD to be exerted in the treatment plant rather than in the stream

How is this accomplished? Create a very rich environment for growth of a diverse microbial community

Basic Ingredients High density of microorganisms (keep organisms in system) Good contact between organisms and wastes (provide mixing) Provide high levels of oxygen (aeration) Favorable temperature, pH, nutrients (design and operation) No toxic chemicals present (control industrial inputs)

Dispersed growth vs Fixed Growth Dispersed Growth – suspended organisms Activated sludge Oxidation ditches/ponds Aerated lagoons, stabilization ponds Fixed Growth – attached organisms Trickling filters Rotating Biological Contactors (RBCs)

Activated Sludge Process in which a mixture of wastewater and microorganisms (biological sludge) is agitated and aerated Leads to oxidation of dissolved organics After oxidation, separate sludge from wastewater Induce microbial growth Need food, oxygen Want Mixed Liquor Suspended Solids (MLSS) of 3,000 to 6,000 mg/L

Activated Sludge w/w Mixed Return Activated Sludge Liquor (RAS) Air Treated w/w td = approximately 6 - 8 hr Long rectangular aeration basins Air is injected near bottom of aeration tanks through system of diffusers Controlled by wasting a portion of microorganisms Secondary clarifier Waste Activated Sludge (WAS) Discharge to River or Land Application

Activated sludge East Lansing WWTP

Secondary Clarifier East Lansing WWTP

Activated Sludge Design Major design parameter: food to microorganism ratio:

Activated Sludge Design td = approximately 6 - 8 hr Long rectangular aeration basins Air is injected near bottom of aeration tanks through system of diffusers Aeration system used to provide mixing MLVSS and F/M controlled by wasting a portion of microorganisms

F/M Parameter Low F/M (low rate of wasting) starved organisms more complete degradation larger, more costly aeration tanks more O2 required higher power costs (to supply O2) less sludge to handle High F/M (high rate of wasting) organisms are saturated with food low treatment efficiency

Trickling Filters Rotating distribution arm sprays primary effluent over circular bed of rock or other coarse media Air circulates in pores between rocks “Biofilm” develops on rocks and micro- organisms degrade waste materials as they flow past Organisms slough off in clumps when film gets too thick

Trickling Filters Filter Material

Trickling Filters Not a true filtering or sieving process Material only provides surface on which bacteria to grow Can use plastic media lighter - can get deeper beds (up to 12 m) reduced space requirement larger surface area for growth greater void ratios (better air flow) less prone to plugging by accumulating slime

Trickling Filters

Trickling Filter Plant Layout

Rotating Biological Contactors Called RBCs Consists of series of closely spaced discs mounted on a horizontal shaft and rotated while ~40% of each disc is submerged in wastewater Discs: light-weight plastic Slime is 1-3 mm in thickness on disc

Rotating Biological Contactors

Rotating Biological Contactors Aeration Shearing of excess microorganisms Attached microorganisms pick up organics Film mixes with wastewater

Rotating Biological Contactors Primary Settling Sludge Treatment Secondary Sludge Treatment

Low-tech solutions Aerobic ponds Facultative ponds Anaerobic ponds

Aerobic ponds Shallow ponds (<1 m deep) Light penetrates to bottom Active algal photosynthesis Organic matter con-verted to CO2, NO3-, HSO4-, HPO42-, etc.

Facultative ponds Ponds 1 - 2.5 m deep td = 30 - 180 d not easily subject to upsets due to fluctuations in Q, loading low capital, O&M costs Aerobic Anaerobic Facultative Facultative zone: aerobic during day (photosynthesis occurs) anaerobic at night (respiration) Rely on wind action for reaeration wastewater enters from bottom

Oxidation Ditches

Anaerobic Ponds Primarily used as a pretreatment process for high strength, high temperature wastes Can handle much high loadings 2 stage: Acid fermentation: Organics  Org. acids Methane fermentation Org. Acids  CH4 and CO2

Land and Wetland Application Spray irrigation and infiltration Overland flow Wetlands Source: Environmental Science, 4th ed., B.J. Nebel and R.T. Wright, Prentice- Hall, N.J., c. 1981

Spray irrigation Usually follows oxidation ponds, aerated lagoons Secondary Treatment Flooding, channeling spray irrigation Usually follows oxidation ponds, aerated lagoons Application leads to filtering, biological degradation, ion exchange, sorption, photodegradation Need about 1 acre/100 people

Spray irrigation Problems climate pathogens need buffer zone Source: Environmental Science, 4th ed., B.J. Nebel and R.T. Wright, Prentice-Hall, N.J., c. 1981

Overland flow Water irrigated onto long narrow fields Secondary Treatment Application to land slopped at 2-8% Water irrigated onto long narrow fields Use grasses that take up large amounts of nitrogen Underlying soil should be fairly impervious

Overland Flow: Emmitsburg, MD Treats 1 MGD on 200 acres Settling pond then irrigated Fields planted with reed canary grass Below ~1 ft topsoil is compacted clay Source: Environmental Science, 4th ed., B.J. Nebel and R.T. Wright, Prentice-Hall, N.J., c. 1981

Overland Flow: Emmitsburg, MD W/W applied to one side of field, percolates through topsoil to a collecting gutter Water in gutter (clear and nutrient-free) Collected in another reservoir and spray-irrigated onto forage crops Source: Environmental Science, 4th ed., B.J. Nebel and R.T. Wright, Prentice-Hall, N.J., c. 1981

Overland Flow: Emmitsburg, MD Land for irrigation was donated by townsperson Why? What were the benefits of such a project? What would be the concerns? Source: Environmental Science, 4th ed., B.J. Nebel and R.T. Wright, Prentice-Hall, N.J., c. 1981

Overland Flow: Emmitsburg, MD Advantages free water free nutrients plants can be fed to animals low-cost low-maintenance water meets discharge regulations (NPDES) Disadvantages will not work in cold climates pathogen dispersion in air need buffer zones need large amount of land

Wetlands Use of natural or artificial wetlands (From: http://www.city.pg.bc.ca/finished.htm) Wetlands Use of natural or artificial wetlands Floating plants act as filters and support for bacteria (From: Environmental Science, 4th ed., B.J. Nebeland R.T. Wright, Prentice-Hall, N.J., © 1981)

Facility Options Considerations for wastewater treatment facility options … 

Facility Options Considerations for wastewater treatment facility options costs capital operation and maintenance (including energy) availability of space degree of treatment required by NPDES permit municipal or municipal plus industrial flowrate

Facility Options Considerations for wastewater treatment facility options distance from residential properties problems with: odors, flies, other nuisances agricultural usage or land application options presence of pathogens experience of design engineers

PERLAKUAN PRIMER Pemisahan fisik bahan organik tersuspensi dalam bak pengendapan untuk mengurangi kebutuhan oksigen biologis (BOD).

PERLAKUAN SEKUNDER Degradasi oleh mikroba untuk mengurangi kandungan senyawa organik. Dua cara: Degradasi anaerobik dalam sludge tank / activated sludge tank Degradasi aerobik menggunakan trickling bed filter.

KEBUTUHAN OKSIGEN Kebutuhan oksigen mencerminkan proses biologis. Dinyatakan dalam Biological Oxygen Demand (BOD) yang merupakan kebutuhan oksigen untuk merombak senyawa organik dalam limbah cair selama 5 hari pada suhu 20oC.

KEBUTUHAN OKSIGEN 2 Dinyatakan juga dalam bentuk Chemical Oxygen Demand (COD) yang merupakan jumlah oksigen ang diperlukan untuk mengoksidasi senyawa organik selama. Perbedaan BOD dan COD mencerminkan efisiensi proses biologi yang dilakukan.

PERLAKUAN TERSIER Untuk menghilangkan sisa senyawa organik dan mineral (biasanya berbeaya tinggi dan tidak selalu dibutuhkan). Fosfat dapat diendapkan dengan flokulasi menggunakan garam yang mengandung aluminium, besi atau kalsium. Mikroba pathogen dapat dihilangkan dengan khlorinasi atau penyinaran UV. Arang aktif dapat digunakan untuk menghilangkan senyawa oganik rekalsitran.

PARAMETER HASIL OLAHAN BOD (Biological Oxigen Demand) COD (Chemical Oxigen Demand) SS (Suspended Solid) TSS (Total Suspended Solid) N-Ammonium (Nitrogen Removal) N-Nitrit (Nitrogen Removal) N-Nitrat (Nitrogen Removal) P-Phospat (Phospourus Removal) pH